The present disclosure relates to communicating over access networks or access communication networks.
The current state of the art considers separately the handover procedures from the session establishment procedures, for example in 3rd Generation Partnership Project (3GPP) and Internet Engineering Task Force (IETF).
In particular, the current state of the art considers separately the problems of network based network discovery and selection and handover optimizations, e.g. 3GPP, and IETF.
Related to handover, the following two conceptual mechanisms for handover are defined for the network based network discovery and selection: First, the network discovery and selection decision is made independent on the triggering or of the handover operation. Second, the network discovery and selection decision is made highly triggered by the trigger or of the handover operation.
In the first case, the network makes the network discovery and selection decision and transmits the information to the mobile device dependent on other external parameters. When a handover is triggered by the mobile device due to various external factors, the handover operation is executed. This presumes that no proactive procedure is executed on the target access network before the handover trigger.
In certain scenarios, the network entity making the network selection decision is aware with a very high probability of the access network to which the handover will be executed, not at the moment of the handover trigger because this is dependent on the mobile device. In these cases, the network selection can be followed by an indication to the target access network in order to prepare for a future handover. Because of this preparation, the time critical execution of the handover may be minimized.
In the second case, the network makes the network discovery and selection decision and transmits it to the mobile device only after the handover is triggered by the mobile device. In this case, all the procedures related to the handover are executed after the handover trigger, namely after the network receives the network discovery and selection request from the mobile device which is after the handover was triggered.
Even though the handover trigger may be proactive, e.g. based on a rapid decrease of signal strength, all the procedures related to the handover are executed after the event happens.
For both cases, only after the event that an imminent handover is available at the mobile device, the procedures for the handover are executed, e.g. in the 3GPP specification the procedures for a handover contain a preparation phase and a handover execution phase. The procedures for the handover have to be faster than the loss of connectivity to the source access network. Otherwise, there is an interruption in service due to the handover.
For example, in the 3GPP Evolved Packet Core (EPC) architecture, the problem may be presented as following. The Access Network Discovery and Selection Function (ANDSF) transmits the new network discovery and selection information to the mobile device depending on various factors independent whether a handover event is available at the mobile device. Even though the ANDSF is aware that one or more of the access networks are highly probable to be selected by the mobile device in the near future and that a handover procedure may be executed, no indication is transmitted to any other network entity in order to prepare this future handover. When the handover event happens at the mobile device, it executes the handover procedures without having any proactive procedure executed. Therefore, it executes all the re-selection procedures, preparation phases and handover execution phases after the handover trigger. If the attachment to the target access network takes a long period of time, e.g. because of 3GPP accesses—UTRAN, GERAN, E-UTRAN, and the connectivity to the source access network may be fast lost (e.g. WiFi accesses), then a reduction of the duration of the procedures executed after the handover trigger may be to be considered.
For example, in the IEEE 802.21 Media Independent Handover (MIH) architecture, two types of operations are defined. For the first, the handover is controlled by the mobile device while in the second it is controlled by the network. In the mobile device controlled scenario, the mobile device detects the handover event. Then, the mobile device requests the network discovery and selection information from the network. In this case, all the handover related procedures are executed after the handover trigger, even if they contain some proactive procedures over the target access network.
In the network controlled handover, the network MIHF executes some proactive procedures. Only afterwards, it transmits a handover command to the mobile device. In this case, the handover decision is not made by the mobile device and the handover trigger is received from the network. Thus, the procedure of executing the proactive operations and the handover procedure are tightly coupled. The handover has to be and is executed immediately after receiving of the information from the network. As a result, it is not based on event triggers which may be received only by the mobile device, e.g. Link Down or Link Going Down.
Therefore, neither the 3GPP nor the MIH consider that any procedure may be executed on the target access network prior to the handover trigger which may be an active or proactive trigger remaining that all the preparation procedures on the target access network and the handover execution procedure to be executed after this trigger.